Zollinger‑Ellison syndrome (gastrin‑independent) - Symptoms, Causes, Treatment & Prevention

Overview

Zollinger‑Ellison syndrome (ZES) is a rare disorder characterized by one or more gastrin‑producing neuroendocrine tumors (gastrinomas) that typically arise in the duodenum or pancreas. In the classic form, these tumors secrete excess gastrin, leading to extreme stomach acid production. The gastrin‑independent variant, however, refers to cases where the clinical picture of ZES (peptic ulcer disease, acid hypersecretion, diarrhea) is present but serum gastrin levels are normal or only mildly elevated. This can occur when tumors produce other acid‑stimulating substances or when acid‑secreting cells become hyper‑responsive.

Although ZES overall affects approximately 1 in 1–3 million people per year worldwide, the gastrin‑independent form is even rarer, representing roughly 5–10 % of all ZES cases (Mayo Clinic, 2023). It can develop at any age but most commonly appears in adults between 30 and 60 years old, with a slight male predominance.

Symptoms

The symptom pattern mirrors classic ZES but tends to be more variable because gastrin levels are not markedly elevated. Common manifestations include:

Gastrointestinal symptoms

• Refractory peptic ulcers – multiple ulcers in the stomach and duodenum that fail to heal with standard therapy.
• Upper abdominal pain – burning or gnawing pain that may improve with food (ulcer‑related) or worsen (acid reflux).
• Heartburn / gastro‑esophageal reflux disease (GERD) – due to excessive acid spilling into the esophagus.
• Diarrhea – often watery, occurring several times a day; may be caused by acid inactivation of pancreatic enzymes.
• Steatorrhea (fatty stools) – malabsorption of fat secondary to pancreatic enzyme destruction.
• Nausea and vomiting – especially after meals.

Systemic symptoms

• Weight loss – from malabsorption and reduced oral intake.
• Fatigue – due to anemia from chronic gastrointestinal bleeding.
• Muscle cramps / tetany – from low serum magnesium or calcium caused by acid‑induced renal losses.

Signs suggesting a gastrin‑independent pattern

• Normal fasting gastrin (<100 pg/mL) despite severe ulcer disease.
• Absence of hyperparathyroidism (MEN‑1 patients often have high gastrin).
• Marked response to acid‑suppression therapy but lack of gastrin elevation on labs.

Causes and Risk Factors

Zollinger‑Ellison syndrome originates from **gastrinomas**, which are neuroendocrine tumors (NETs) arising from enterochromaffin‑like (ECL) cells. In the gastrin‑independent variant, the pathophysiology may involve:

• Co‑secretion of other hormones (e.g., vasoactive intestinal peptide, secretin) that stimulate parietal cells.
• Paracrine activation of acid‑secreting pathways within the gastric mucosa.
• Rare genetic mutations that alter tumor secretory profiles.

Key risk factors

• Multiple endocrine neoplasia type 1 (MEN‑1) – a hereditary syndrome (mutations in the MEN1 gene) that predisposes to gastrinomas, pituitary tumors, and hyperparathyroidism. Approximately 20‑30 % of ZES patients have MEN‑1; gastrin‑independent cases are less common in MEN‑1.
• Family history of neuroendocrine tumors – inherited mutations in genes such as CDKN1B or VHL may increase susceptibility.
• Age and gender – slight male predominance; peak incidence in the fourth to sixth decade.
• Chronic Helicobacter pylori infection – while not a direct cause, it can exacerbate ulcer disease and mask the diagnosis.

Diagnosis

Diagnosing gastrin‑independent ZES requires a high index of suspicion because serum gastrin may be normal. The work‑up combines clinical, imaging, and functional studies.

1. Laboratory evaluation

• Fasting serum gastrin – measured after at least 8 hours of fasting; values <100 pg/mL are typical in gastrin‑independent disease.
• Secretin stimulation test – paradoxical rise in gastrin after intravenous secretin suggests gastrinoma even with normal baseline levels.
• Stool pH – low pH (<2.5) indicates hyperacidic environment.
• Electrolytes & renal function – monitor magnesium, calcium, and bicarbonate for acid‑related losses.

2. Imaging studies

• Endoscopic ultrasound (EUS) – high‑resolution imaging of the pancreas and duodenum; can detect tumors as small as 2–3 mm.
• Multiphasic contrast‑enhanced CT or MRI – evaluates tumor size, local invasion, and metastatic spread (especially to the liver).
• Somatostatin receptor scintigraphy (Octreoscan) or ^68Ga‑DOTATATE PET/CT – highly sensitive for neuroendocrine tumors, including gastrinomas that are not hyper‑gastrinergic.

3. Endoscopic assessment

• Upper endoscopy (EGD) – identifies multiple or refractory peptic ulcers; biopsies rule out H. pylori and malignancy.
• pH monitoring (24‑hour esophageal/duodenal) – confirms continuous acid hypersecretion.

4. Histopathology

If a tumor is resected, pathology confirms a well‑differentiated neuroendocrine tumor (NET G1–G2) with immunohistochemical staining for chromogranin A, synaptophysin, and sometimes gastrin or other peptides.

Treatment Options

Management aims to control acid hypersecretion, remove or control the tumor, and address nutritional deficits.

1. Acid‑suppression therapy (first line)

• High‑dose proton pump inhibitors (PPIs) – e.g., omeprazole 60 mg daily or esomeprazole 40 mg daily, titrated to symptom control. PPIs are effective in >90 % of patients and are the cornerstone of therapy (Cleveland Clinic, 2022).
• Histamine‑2 receptor antagonists (H2RAs) – may be added for breakthrough symptoms, but are less potent than PPIs.
• Long‑term PPI use requires monitoring for hypomagnesemia, vitamin B12 deficiency, and osteoporosis.

2. Surgical management

• Localized tumor resection – duodenal or pancreatic enucleation; provides potential cure when disease is limited.
• Pancreaticoduodenectomy (Whipple procedure) – reserved for large, invasive, or multiple tumors.
• Debulking surgery – reduces tumor burden when complete resection is impossible; improves symptom control.

3. Medical therapies for unresectable or metastatic disease

• Somatostatin analogues (octreotide, lanreotide) – suppress hormone secretion and can shrink tumors.
• Targeted therapies – everolimus (mTOR inhibitor) or sunitinib (tyrosine‑kinase inhibitor) for progressive NETs.
• Peptide receptor radionuclide therapy (PRRT) – ^177Lu‑DOTATATE delivers radiation directly to somatostatin‑receptor–positive cells.
• Cytotoxic chemotherapy – streptozocin‑based regimens are used sparingly for high‑grade disease.

4. Nutritional and lifestyle measures

• Small, frequent meals low in simple carbohydrates and high in protein.
• Avoidance of alcohol, caffeine, nicotine, and NSAIDs, which aggravate ulcer disease.
• Supplementation with calcium, vitamin D, and magnesium if deficiencies develop.
• Routine monitoring of bone density (DEXA) because chronic acid suppression may affect calcium balance.

Living with Zollinger‑Ellison Syndrome (Gastrin‑Independent)

Long‑term disease control requires a partnership between the patient, gastroenterologist, endocrinologist, and surgeon.

Daily management tips

• Medication adherence – take PPIs exactly as prescribed; never skip doses.
• Track symptoms – keep a diary of pain, heartburn, stool consistency, and any new bleeding.
• Regular labs – at least every 6–12 months check gastrin, chromogranin A, magnesium, calcium, vitamin B12, and liver function.
• Imaging surveillance – annual or biennial CT/MRI or ^68Ga‑DOTATATE PET to detect recurrence.
• Vaccinations – if undergoing chemotherapy or PRRT, receive pneumococcal, influenza, and hepatitis B vaccines.
• Psychosocial support – consider counseling or support groups for chronic illness coping.

Dietary guidance

1. Consume low‑acid foods (bananas, oatmeal, non‑citrus fruits).
2. Include protein‑rich sources (lean meat, fish, beans) to offset malabsorption.
3. Limit high‑fat meals that can exacerbate steatorrhea.
4. Stay hydrated; oral rehydration solutions with electrolytes help replace magnesium and bicarbonate losses.

Prevention

Because ZES is largely driven by sporadic tumors, primary prevention is limited. However, risk reduction strategies include:

• **Genetic counseling** for families with MEN‑1 or other NET‑predisposing mutations; consider testing for at‑risk relatives.
• **Screening endoscopy** for known MEN‑1 carriers beginning in adolescence, per NIH recommendations.
• **Eradication of H. pylori** infection, which can worsen ulcer disease and obscure diagnosis.
• **Avoid chronic use of ulcer‑inducing drugs** (NSAIDs, chronic steroids) that can trigger ulcer formation and mask underlying ZES.

Complications

If left untreated or poorly controlled, gastrin‑independent ZES may lead to serious health problems:

• Severe peptic ulcer disease – perforation or bleeding requiring emergency surgery.
• Gastrointestinal hemorrhage – chronic blood loss causing iron‑deficiency anemia.
• Esophageal strictures – from chronic reflux, leading to dysphagia.
• Malabsorption syndromes – leading to weight loss, vitamin deficiencies, and osteoporosis.
• Metastatic neuroendocrine tumor spread – especially to the liver, lungs, or bone, which worsens prognosis.
• Electrolyte disturbances – hypomagnesemia, hypocalcemia, and metabolic alkalosis from chronic acid loss.

When to Seek Emergency Care

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References: Mayo Clinic. Zollinger‑Ellison syndrome. 2023; link. Cleveland Clinic. Gastrinomas and ZES. 2022; link. NIH National Institute of Diabetes and Digestive and Kidney Diseases. Neuroendocrine Tumors Fact Sheet. 2024; CDC. Rare Disease Data. 2023; WHO. Classification of Tumors of the Digestive System. 2023.